---
title: "Complex compounds vs double salts"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:complex-vs-double"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/complex-vs-double
site: BCT Engineering
---

# Complex compounds vs double salts

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2073 Bhadra, 1 marks; 2068 Magh, 2 marks (asked 2 times)
- Video: [Coordination Compounds | Class 12 Chemistry | Coordination Compounds and Double Salts | iWiz Divya](https://www.youtube.com/watch?v=vmH2OGTmz9M) — Iwiz Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/complex-vs-double
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Differentiate between complex compounds and double salts.

## Short answer

Complex compounds have a central metal ion bound to ligands by coordinate bonds and remain intact in solution; double salts are combinations of simple salts that completely dissociate into all ions in water. Example: K₄[Fe(CN)₆] is a complex, while Mohr's salt is a double salt.

## Answer

| Basis | Complex compound | Double salt |
|---|---|---|
| Formation | Central metal ion bonded to ligands by coordinate bonds | Two simple salts combined in a fixed ratio |
| Stability in solution | Complex ion remains intact | Breaks into its constituent ions |
| Ions | Complex ion and counter ion | All ions of both salts |
| Properties | New properties (colour, magnetism) different from the components | Properties of the component salts |
| Test | Metal in complex ion gives no normal test | Gives tests of all ions |
| Example | K₄[Fe(CN)₆] | Mohr's salt, KAl(SO₄)₂·12H₂O |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A complex compound is formed by
   A. two simple salts crystallising together
   B. a central metal ion bonded to ligands by coordinate bonds
   C. ionic transfer only
   D. a hydrogen bond
   Answer: B. Double salts are two salts combined. (Key point: Formation)

2. In solution, a complex ion
   A. breaks into constituent ions
   B. evaporates
   C. remains intact
   D. becomes a neutral atom
   Answer: C. A double salt breaks up. (Key point: Solution behaviour)

3. Metal in complex ion gives
   A. all normal tests
   B. only flame test
   C. precipitate always
   D. no normal test
   Answer: D. Double salts give tests for all ions. (Key point: Test)

4. Which is a double salt?
   A. Mohr's salt
   B. K4[Fe(CN)6]
   C. [Cu(NH3)4]SO4
   D. [Co(NH3)6]Cl3
   Answer: A. Mohr's salt and KAl(SO4)2.12H2O. (Key point: Example)

## Related in Engineering Chemistry

- [Complex vs double salts; EAN of Fe(CN)₆](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Acomplex-double-ean) — Engineering Chemistry, chapter 6
- [Double salt vs complex salt; Werner's theory](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Adouble-complex-werner) — Engineering Chemistry, chapter 6, asked 5×
- [Colour of Ti³⁺ compounds vs zinc compounds](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ati3-zn-colour) — Engineering Chemistry, chapter 5
- [Colour of Ti³⁺ vs Ti⁴⁺ compounds](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ati3-ti4-colour) — Engineering Chemistry, chapter 5